The present invention relates generally to boring tools and more particularly to self-feeding boring tools adapted for machining relatively large diameter holes in wood or like materials.
The boring tool of the present invention comprises a body having a driving shaft associated therewith, a plurality of cutting elements secured to and projecting forwardly from one side of the body and threaded self-feeding means operative to advance the boring tool into and through the workpiece. The cutting depth of the cutting elements is proportioned to the pitch of the threads of the self-feeding means in such a manner that a continuous feed of the self-feeding means into the workpiece occurs. In the absence of such a proportioned relationship, the self-feeding means would undergo a cyclical movement alternating between feed and shearing action as it advances into the workpiece. Accordingly, by proportioning the cutting depth of the cutting elements to the pitch of the threads of the self-feeding means, excessive axial loading on the self-feeding means is substantially reduced or eliminated. Also, the proportioning of the cutting depth will insure that both the cutting elements and the self-feeding means operate in unison to provide substantially the same rate of feed, and thus the power required to rotationally drive the boring tool will be reduced.
Additionally, the boring tool of the present invention also provides a peripheral curb portion adapted to engage the work surface and provide a sled running effect to further limit any tendency of the cutting elements to increase the feed rate of the tool as well as to assist in preventing sudden breakthrough as the boring tool approaches the backside of the workpiece.
Also, in order to further enhance the cutting action of the present invention, the retaining means for securing the body to the associated driving shaft is positioned so as to urge the self-feeding means into close proximity with an adjacent cutting element thereby reducing the possibility that uncut fibers may become lodged between the cutting element and self-feed means and thereby impair or otherwise hamper advancement of the boring tool through the workpiece.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.